Study On Microstructure And Properties Of Pure Aluminum Remelted By Ti And Zr

Aluminum and aluminum alloy are widely used in industry,but the mechanical properties sometimes do not meet the requirements.It is convenient to improve the mechanical properties by adding refiners to refine the grains.At present,due to the decrease of aluminum resources,it is urgent to develop aluminum and aluminum alloy recycling.The recovery process needs to be remelted.Whether the grain refinement effect after remelting is long-term or not directly affects the performance of aluminum recovery.At the same time,the corrosion resistance of alloy determines the service life to a certain extent,as well as the long-term safe and stable use.In this paper,the effects of Ti,Zr compound addition and remelting on the microstructure,mechanical properties and corrosion properties of alloy were studied.Three heterogeneous nucleation cores,Al₃Ti,Al₃Zr and Al₃（Ti,Zr）,can be formed when Ti and Zr are added together,which can jointly promote grain refinement.Al₃（Ti,Zr）cannot be formed when Ti and Zr are added to pure aluminum alone,and the refining effect is relatively poor.The refining effect of Ti is better than that of Zr.When0.5%Ti and 0.3%Zr were added,the average grain size decreased to 77μm,the tensile strength increased to 78.87mpa,and the elongation increased to 52.2%.When 0.1%Ti and 0.5%Zr are added,the higher Zr content is easy to agglomerate the Al₃Zr,reduce the effective nucleation core,reduce the small-size Al₃Zr,and only form a small amount of Al₃Ti and Al₃（Ti,Zr）,so the refinement effect fades.Compared with the alloy with Ti and Zr added alone,the grain refinement of the alloy with Ti and Zr added together has less degradation.Because Al₃（Ti,Zr）is easy to dissolve and form Al₃Ti and Al₃Zr,there are still many nucleating particles after multiple remelting.The alloy with Ti content higher than Zr content has less grain refinement degradation,because the refining effect of Al₃Ti is longer.As a result of Ostwald aging,the small nucleation core is reduced,and Al₃Zr is easy to agglomerate,which leads to the decrease of mechanical properties of the alloy after multiple remelting.When 0.1%Ti and 0.5%Zr are added,Al₃Zr tends to agglomerate with the increase of remelting times,and forms cubic and long strip like coarse phase,while small-size Al₃Zr decreases,so the refinement effect fades.The Al₃Fe and Si impurities which are easy to be introduced after remelting will also decrease the strength and plasticity of the alloy.With the increase of Ti or Zr content,the corrosion resistance of the alloy decreased gradually.As the cathode phase,Al₃Ti,Al₃Zr and Al₃（Ti,Zr）particles increased,the aluminum matrix gradually dissolved.After multiple remelting,the corrosion resistance of the alloy decreased because of the introduction of Al₃Fe and Si impurities,and the coarsening of the grains reduced the compactness of the passivation film.Although Ostwald ripening and Al₃Zr agglomeration reduced the second phase,the overall corrosion resistance decreased.The corrosion products are Al（OH）₃with cracks protruding from Al matrix and Al₂O₃with thin films.The main form of corrosion is pitting.The larger pitting is due to the fact that part of the larger cathode phase falls off the substrate due to the dissolution of the surrounding Al matrix as an anode.